1. Field of the Invention
The present invention relates to a driving-force control apparatus for a vehicle having an engine and a transmission, the driving-force control apparatus including driving-force control means for determining a state of a road surface on which the vehicle is running and for controlling a driving force of the vehicle based on the determined state of the road surface.
2. Description of the Related Art
Japanese Patent Application Laid-open No. 6-289039 (JP '039) discloses a slip-amount calculating apparatus for a vehicle. JP '039 teaches a feature wherein if all of the rotational speed sensors of the four wheels are working normally, the slip amount is calculated based on the average value of the rotational speeds of the right and the left idler wheels and the average value of the rotational speeds of the right and the left driving wheels. If the rotational speed sensor of the right front wheel or the rotational speed sensor of the right rear wheel is not working normally, the slip amount is calculated based on the rotational speed of the left front wheel and the rotational speed of the left rear wheel. If the rotational speed sensor of the left front wheel or the rotational speed sensor of the left rear wheel does not work normally, the slip amount is calculated based on the rotational speed of the right front wheel and the rotational speed of the right rear wheel.
Japanese Patent Application Laid-open No. 11-63209 (JP '209) discloses an automatic-transmission controlling apparatus for a vehicle which inhibits the up-shifting of gears from the second gear to the third gear if the driving wheels slip when the vehicle starts on ice. The automatic-transmission controlling apparatus detects the slip rate of the torque converter based on the engine speed and the number of revolutions of the input shaft of the automatic transmission. If the slip rate exceeds, for example, 102%, and the driving force is transmitted in the opposite direction from the side of the driving wheels to the side of the engine, the controlling apparatus determines that a pseudo slip state caused by the locking and the unlocking of the driving wheels has occurred, and the controlling apparatus cancels the inhibition of the up-shifting of gears by the automatic transmission.
Japanese Utility Model Application Laid-open No. 63-183446 (JP '446) discloses an abnormal-running preventing apparatus for backward motion. JP '446 teaches a feature wherein if the reverse switch is turned on and, at the same time, the degree or extent the throttle opens increases rapidly, the abnormal-running preventing apparatus cuts the fuel to the engine to reduce the driving force.
Japanese Utility Model Application Laid-open No. 1-95550 (JP '550) discloses a travel-safety apparatus for a vehicle. JP '550 teaches a feature wherein a threshold of the vehicle speed for the reverse gear and a threshold of the engine speed for the reverse gear are set to be lower than the threshold for any other gear. If the reverse gear is selected, and, at the same time, at least one of the vehicle speed and the engine speed exceeds the corresponding threshold, the travel-safety apparatus cuts the fuel to the engine to reduce the driving force.
The slip-amount calculating apparatus for a vehicle disclosed in JP '039 suffers from a deficiency wherein if all of the wheel speed sensors provided for the four wheels are working abnormally, a determination as to the road-surface conditions cannot be made.
The automatic-transmission controlling apparatus for a vehicle disclosed in JP '209 suffers from a deficiency wherein the apparatus inhibits the up-shifting of gears if it is determined that the road surface is a low-friction-coefficient road surface. The apparatus, however, does not inhibit the down-shifting of gears even with the same determination. Accordingly, the driving force may occasionally increase due to a down-shifting of gears. As such, if the vehicle is running in snowy conditions, an increase in the driving force may cause the driving wheel to be buried in the snow, resulting in the vehicle becoming stuck in the snow.
The abnormal-running preventing apparatus for backward motion disclosed in JP '446 and the travel-safety apparatus for a vehicle disclosed in JP '550 suffer from a deficiency wherein cutting of the fuel supply is executed only white the reverse gear is selected. For this reason, if any forward gear is selected, the excessive driving force generated on a low-friction-coefficient road surface may cause the vehicle to get stuck.